Transmission of data or information signals is generally achieved through modulation of a carrier signal. The type of modulation, for example, may be amplitude modulation (AM), frequency modulation (FM), or phase modulation. Any of the foregoing modulations can be used depending on the application of the transmission.
A class of implantable medical devices known in the art are small microstimulators and/or sensors. These small microstimulators or sensors, which are hereafter referred to as BION™ devices, are described more fully in the following U.S. Patents: U.S. Pat. No. 5,193,539, entitled “Implantable Microstimulator”; U.S. Pat. No. 5,193,540, entitled “Structure and Method of Manufacture of an Implantable Microstimulator”; U.S. Pat. No. 5,312,439 entitled “Implantable Device Having an Electrolytic Storage Electrode”; U.S. Pat. No. 6,164,284, entitled “System of implantable devices for monitoring and/or affecting body parameters”; U.S. Pat. No. 6,185,452, entitled “Battery-powered patient implantable device”; U.S. Pat. No. 6,208,894, entitled “System of implantable devices for monitoring and/or affecting body parameters ”; U.S. Pat. No. 6,315,721, entitled “System of implantable devices for monitoring and/or affecting body parameters”; Pat. No. 6,564,807, entitled “System of implantable devices for monitoring and/or affecting body parameters, each of which patents are incorporated herein by reference. These BION devices are generally small enough to be implanted in a minimally invasive manner through a lumen of a needle, or a similar sized cannula. These BION devices or microstimulators when implanted can provide the appropriate electrical stimulation to the appropriate nerves or muscles in order to rehabilitate or contribute to the functionality of the intended body parts.
Communication with the microstimulators is achieved through a wireless medium. This communication can be through an electromagnetic or RF link or magnetic/inductive coupling of an external device with the microstimulators. In the case of the inductive coupling the external device generally referred to as a BION control unit (BCU) comprises a charger and a controller wherein the functionality of the charger and the controller may be combined and provided through a multi-turn loop antenna in the form of a single coil. This BCU coil is in turn coupled with the coil in the microstimulator providing the inductive coupling and transmission of power and modulated signal to the microstimulator. The communication between the BCU and the BION is through digital communication or pulse modulation of the carrier signal. It has been realized that the sharpness (rise time and/or fall time) of the square wave digital signal can have a direct effect on the communication and the ability of the BION device to properly receive and decode the modulated digital signal. Although a high power modulation amplifier may be used to overcome the problem associated with the low rise time and fall time of a digital square wave pulse modulated signal, however, this would not be compatible with the low power requirements of an implantable microstimulator. It has been further realized that when utilizing a single coil for the transmission of power and modulated signal to microstimulator the use of a high Q coil provides an optimal transmission of power to the microstimulator. However, the use of a high Q coil will adversely affect the modulation signal in that the rise time and the fall time of the signal will be very slow, therefore resulting in an unreliable reception of the modulated signal by the microstimulator. Thus there is a need in the art for an apparatus that comprises a high Q coil and also provides reliable modulation wherein the rise time and the fall time of the modulation signal are adequate for the proper reception by the microstimulator.
Corresponding numerals indicate corresponding elements throughout the several views of the drawings.